Submerged tree in the Grüner See (Green Lake), Austria. The name “Green Lake” originated because of its emerald-green water. The clean and clear water comes from the snowmelt from the karst mountains. During the winter, the lake is only 1–2 m deep and the surrounding area is used as a county park.However, during the spring, when the temperature rises and the snow melts, the basin of land below the mountains fills with water. The lake reaches its maximum depth of around 1 m from mid-May to June and is claimed to look the most beautiful at this time. In July, the water begins to recede.